This invention relates generally to wireless communication antennas, and more particularly to multi-band antennas for wireless communication devices.
Wireless communication devices typically use multi-band antennas to transmit and receive wireless signals in multiple wireless communication frequency bands, such as Advanced Mobile Phone System (AMPS), Personal Communication Service (PCS), Personal Digital Cellular (PDC), Global System for Mobile communications (GSM), Code Division Multiple Access (CDMA), etc. Because of its compact size and multi-band performance, a planar inverted F-antenna (PIFA) represents a common multi-band antenna for wireless communication devices. PIFAs typically comprise a radiating element spaced from an antenna ground plane. Because the spacing between the radiating element and the ground plane impacts the impedance matching associated with the multi-band antenna, a PIFA typically includes additional impedance matching circuitry that optimizes the impedance matching for the desired frequency range(s) of the antenna. However, due to the wide range of frequencies covered by a multi-band PIFA, the impedance matching is only truly optimal for some of the frequency bands. As such, the antenna does not have optimal impedance matching for at least one other frequency band.
Parasitic elements that modify the impedance matching to improve antenna performance are known. However, while the parasitic element may improve antenna performance in one of the wireless communication frequency bands, the parasitic element typically adversely impacts the performance of the antenna in the other wireless communication frequency band(s).